One construction of a slant plate type compressor, particularly a wobble plate type compressor, with a variable capacity mechanism which is suitable for use in an automotive air conditioner is disclosed in U.S. Pat. No. 3,861,829 issued to Roberts et al. Roberts et al. '829 discloses a wobble plate type compressor which has a cam rotor driving device to drive a plurality of pistons. The slant or inclined angle of the slant surface of of the wobble plate is varied to change the stroke length of the pistons which changes the displacement of the compressor. Changing the incline angle of the wobble plate is effected by changing the pressure difference between the suction chamber and the crank chamber. This pressure difference is effected by adjusting the pressure in the crank chamber.
Roberts et al. '829 discloses a capacity adjusting mechanism used in a wobble plate type compressor. As is typical in this type of compressor, the wobble plate is disposed at a slant or incline angle relative to the drive axis, nutates but does not rotate, and drivingly couples the pistons to the drive source. This type of capacity adjusting mechanism, using selective fluid communication between the crank chamber and the suction chamber, can be used in any type of compressor which uses a slanted plate or surface in the drive mechanism. For example, U.S. Pat. No. 4,664,604 issued to Terauchi discloses this type of capacity adjusting mechanism in a swash plate type compressor. The swash plate, like the wobble plate, is disposed at a slant angle and drivingly couples the pistons to the drive source. However, while the wobble plate only nutates, the swash plate both nutates and rotates. The term slant plate type compressor will therefore be used to refer to any type of compressor, including wobble and swash plate types, which use a slanted plate or surface in the drive mechanism.
Referring to FIG. 1, a construction of a wobble plate type compressor is shown. The compressor includes compressor housing 1 having cylinder block 2 which is provided with a plurality of cylinder 22 and crank chamber 3. Cylinder head 4 is mounted on one end portion of cylinder block 2 through valve plate 5. Drive shaft 6 is rotatably supported on tubular extension 11 through bearing 7. Tubular extension 11 is formed on the compressor at its end opposite valve plate 5. The inner terminal end of drive shaft 6 exends within crank chamber 3 and is rotatably supported in central hole 21 of cylinder block 2 through bearing 8.
Rotor 9 is connected to drive shaft 6 and is rotatable with the drive shaft. Rotor 9 engages one side surface of inclined plate 10 through hinge mechanism 91. The angle of inclined plate 10 with respect to drive shaft 6 can be adjusted by hinge mechanism 91. The other side surface of inclined plate 10 is disposed on wobble plate 12 which is rotatably supported on inclined plate 10. Thrust bearing 13 is disposed between inclined plate 10 and wobble plate 12. Guide bar 14 axially extends within crank chamber 3 and connects one end of compressor housing 1 with cylinder block 2. The lower end portion of wobble plate 12 engages guide bar 14 so that wobble plate 12 can reciprocate along guide bar 14 while rotational motion of wobble plate 12 is prevented.
A plurality of pistons 15 are slidably fitted within respective cylinders 22 and are connected to wobble plate 12 through connecting rods 16. Cylinder head 4 is divided into suction chamber 4a and discharge chamber 4b.
Control valve mechanism 17, shown in FIG. 2, is disposed in suction chamber 4a and controls the opening and closing of passageway 18 which communicates between crank chamber 3 and suction chamber 4a. Control valve mechanism 17 includes first casing 171, second casing 172 which is fixed on one end surface of first casing 171, and bellows 173 which is disposed within the interior of first casing 171 and is held in position by coil spring 174. Bellows 173 is provided with valve portion 173a at its outer end surface. A coil spring (not shown) is disposed within bellows 173 to control the expansion and contraction of bellows 173. First casing 171 is provided with first channel 171a at its outer peripheral portion to communicate between the interior of first casing 171 and suction chamber 4a. Second casing 172 is provided with second channel 172a and third channel 172b. Second channel 172a and third channel 172b communicate with crank chamber 3 through passageway 18. Passageway 18 extends through drive shaft 6 as shown in dotted lines in FIG. 1. The arrows illustrate the flow of refrigerant from crank chamber 3 to suction chamber 4a. Thus, crank chamber 3 and suction chamber 4a communicate with one another through control valve mechanism 17.
The operation of control valve mechanism 17 is as follows. If the pressure in suction chamber 4a exceeds a predetermined value as determined by bellows 173, bellows 173 in first casing 171 contracts, and moves valve portion 173a toward the left in the figure. Accordingly, third channel 172b is opened, and crank chamber 3 communicates with suction chamber 4a through passageway 18, second channel 172a, third channel 172b, and first channel 171a. Therefore, the pressure in crank chamber 3, which acts on the rear of the pistons, decreases, and the incline angle of wobble plate 12 increases. As a result, the stroke volume of pistons 15 increases, and the capacity of the compressor also increases.
Conversely, if the pressure in suction chamber 4a is below the predetermined value, bellows 173 in first casing 171 expands, and moves valve portion 173a toward the right in the figure. Accordingly, third channel 172b is closed, and there is no communication between crank chamber 3 and suction chamber 4a. The pressure in crank chamber 3 thus gradually increases due to the leakage of blow-by gas from cylinders 22. Therefore, the pressure on the rear of the pistons increases, and the incline angle of wobble plate 12 decreases. As a result, the stroke volume of pistons 15 decreases, and the capacity of the compressor decreases.
In an automotive air conditioning system which uses the above discussed compressor, if the compressor begins operation when the thermal load in the passenger compartment of the vehicle is large and the engine is driven at high speeds, the pressure in the suction chamber of the compressor is below the predetermined value of the control mechanism. Thus, the capacity of the compressor is inadequate as the suction pressure is less than the predetermined value and there is no fluid communication between the crank chamber and the suction chamber. Due to this fluid communication, the capacity decreases when increased capacity is desired. Therefore, the capacity control mechanism of the compressor operates in spite of the insufficient decrease in the temperature in the passenger compartment of the car. Thus, the ability to cool is not good as in a conventional wobble plate type compressor without a variable capacity mechanism.